This invention relates generally to pleated filters and to pleat fold spacers which are interposed between pleats. More particularly, the invention relates to high efficiency particulate air filters known in the industry by the acronym, HEPA. Such filters as well as many types of filters used for various air filtering purposes use a porous or microporous filter medium known to the art such as various types of paper or sheet material composed of non-woven fibers which may or may not be of cellulose, glass or plastic fibers or mixtures thereof.
Such filters are made by folding filter media into pleats incorporating suitable spacers between the pleats and then enclosing the pleated assembly within a suitable enclosure in a manner which retains the pleated filter assembly in a size and shape which is suitable for the use to which it is put.
The structure and characteristics of HEPA filters, especially as used in the nuclear industry are described in the "Nuclear Air Cleaning Handbook" published by Oak Ridge National Laboratory. ERDA 76-21 (Burchsted, et al - NTIS).
Various types of filters and separators as used in the art are described in U.S. Pat. Nos. 3,321,345, 3,871,851, 4,135,900, 4,147,524 and others.